Designing the Big Boom

It's a dangerous job: Fly a helicopter into the mountains and throw lighted dynamite out the cabin door to produce a controlled avalanche. To make matters worse, half the time the dynamite doesn't explode when it hits the snow, leaving another type of hazard for the people on the ground -- who must trek through this treacherous territory to find the duds or risk injury to innocent people hiking in the area after the snow melts.

"Having 200 kilograms of dynamite in the cabin and some guy in the back with a lighter or some matches always made me feel a little nervous," says Werner Greipl of Heli Rescue Consult.

He thought he could design a better solution.

Explosions without Explosives
Greipl's experience as a helicopter pilot merged with his mechanical engineering background when he developed Avalanche Blast, a device that hangs by a tether a safe distance below the helicopter. It fills a 1.5-meter meteorological balloon at the base of the apparatus with explosive gas. The gases -- oxygen and hydrogen -- are fairly safe to transport in separate canisters. Mixed inside the balloon at a critical proportion, however, the gases become very volatile. When ignition is signaled by remote control, the balloon explodes with a force equivalent to 2 to 4 kilograms of dynamite.

Avalanche Blast hangs a safe distance below the helicopter cabin.

The biggest advantage of Greipl's design is that Avalanche Blast eliminates the need for explosives in the helicopter cabin. Users don't have to grapple with finding unexploded charges, and the balloon material is biodegradable.

Prepping for a Prototype
But getting the design right wasn't easy. Greipl needed a prototype with movable mechanisms to quickly change the canisters of gas during a helicopter pit stop, plus a magazine of eleven latex balloons to automatically load and inflate. In the end, his design had 329 solid metal components.

With limited experience in modeling solids, Greipl began working with Alibre Design. "The importance of designing in a 3D solid modeler like Alibre Design is not only to see clearly how the parts fit together in the final assembly, but also the range of motion of moving parts," he says. "In Avalanche Blast, the mechanics assemble and reassemble to load and unload the canisters. Alibre Design allowed me to create the kinematic concept I had in mind."

The complete Avalanche Blast model in Alibre Design.

After testing the prototype for two seasons around ski resorts and mountain passes in the Dolomite region of Italy, Greipl discovered that Avalanche Blast successfully moved snow at a rate of 80%, a big improvement from dynamite's typical rate of 50%. Greipl's company sold the Avalanche Blast concept to a French manufacturer, TAS, which makes ground-based avalanche control systems and will soon make this airborne method commercially available.

The Avalanche Blast balloon before and after ignition.

"Compared to traditional methods, Avalanche Blast is safer and more environmentally friendly," says Greipl. He believes that should make everyone feel less nervous.

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